JPH1155064A - Wafer and piezoelectric element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric element having a high electric/mechanical coupling coefficient and high temperature stability. SOLUTION: A wafer 1 is a wafer of a lanthanum-gallium-niobate crystal cut along YX1b/α/β. In this case, when the crystal axes of the lanthanum- gallium-niobate crystal are respectively defined as an X axis (electric axis), Y axis (mechanical axis) and Z axis (optical axis), the wafer 1 forms an angle αfrom the Z axis within a YZ plane at -15 deg.<=α<=+25 deg. in counter clockwise direction and forms an angle β from the X axis within an XZ plane at -10 deg.<=β<=+10 deg. in counter clockwise direction by segmentation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter, an oscillator, a delay line, and the like in the field of electronic communication such as a communication device and a mobile phone (a field of radioelectronics and acoustoelectronics).
The present invention relates to a wafer and a piezoelectric element used for a purpose of selecting a specific frequency such as a superposition device.

[0002]

2. Description of the Related Art Conventionally, in the field of electronic communication, a piezoelectric element using a quartz crystal chip (wafer), a lithium niobate crystal chip (wafer),
A piezoelectric element using a lithium tantalate crystal chip (wafer) is known.

Here, a piezoelectric element using a quartz crystal chip (wafer) has a high temperature stability of about 1 ppm / ° C., but has a low electromechanical coupling coefficient.
There is a disadvantage that it is difficult to manufacture a filter having a wider bandwidth and an oscillator having a larger tuning range.

On the other hand, a piezoelectric element of a lithium tantalate crystal chip (wafer) or a lithium niobate crystal chip (wafer) has a high electromechanical coupling coefficient, and is suitable for various wireless devices requiring a wide bandpass band. Widely used in electronic equipment.

[0005]

However, the piezoelectric elements of the lithium niobate crystal chip (wafer) and the lithium tantalate crystal chip (wafer) have low temperature stability.
It is 0 ppm / ° C. or higher, and therefore has drawbacks such that it cannot be used for narrow band and intermediate band devices.

The present invention selects a specific frequency such as a band-pass filter, an oscillator, a delay line, and a superimposing device in the field of electronic communication such as a communication apparatus and a mobile phone (fields such as wireless electronics and acousto-electronics). It is an object of the present invention to provide a new wafer used for an application to be performed.

Another object of the present invention is to provide a piezoelectric element having a high electromechanical coupling coefficient and high temperature stability.

[0008]

In order to achieve the above object, an invention according to claim 1 is a wafer obtained by cutting a lanthanum gallium niobate crystal by a YX1b / α / β cut. When the crystal axes of the gallium-niobate crystals are X-axis (electric axis), Y-axis (mechanical axis), and Z-axis (optical axis), the wafer is placed in the YZ plane.
The angle α from the axis forms −15 ° ≦ α ≦ + 25 ° counterclockwise, and the angle β from the X axis in the XZ plane forms −10 ° ≦ β ≦ + 10 ° counterclockwise. , Is characterized by being cut out.

Further, the invention according to claim 2 provides a lantern
A piezoelectric element using a wafer obtained by cutting a gallium niobate crystal by YX1b / α / β cut, wherein a crystal axis of the lanthanum gallium niobate crystal is set to an X axis.
(Electric axis), Y axis (mechanical axis), and Z axis (optical axis), the wafer has an angle α from the Z axis in the YZ plane of which −15 ° ≦ α ≦ + 25 ° in a counterclockwise direction. None, and the angle β from the X-axis in the XZ plane is −10 ° ≦
It is characterized by being cut out so as to satisfy β ≦ + 10 °.

According to a third aspect of the present invention, in the piezoelectric element according to the second aspect, the wafer has an excitation electrode pair for exciting an elastic wave, and converts the elastic wave propagating through the wafer into an electric signal. And a pair of extraction electrodes for extracting the same in parallel.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a view showing an embodiment of a wafer according to the present invention. Referring to FIG. 1, this wafer 1
Is a lanthanum gallium niobate crystal (La ₃ Ga
_5.6 Nb _0.5 O ₁₄ crystal), that is, so-called langanite cut out by YX1b / α / β cut. Here, α is a rotation angle around the X axis (the cut angle of the crystal in the YZ plane (counterclockwise angle from the Z axis in the YZ plane)), and β is the rotation around the Y axis. Angle (cut angle of the crystal in the XZ plane (counterclockwise angle from the X axis in the XZ plane)). In FIG. 1, X
Y axis when rotated counterclockwise by α around the axis,
The position of the Z axis is indicated by Y ', Z ", and in this state,
The positions of the Z ″ axis and the X axis when rotated counterclockwise by β around the Y axis (more precisely, the Y ′ axis) are indicated by Z ′ and X ′.

In this case, the wafer 1 of the present invention is arranged such that the cut angle α satisfies −15 ° ≦ α ≦ + 25 °, and the cut angle β satisfies −10 ° ≦ β ≦ + 10 °. , Langanaite is cut out.

In the present invention, when the wafer 1 of YX1b / α / β cut lanthanum gallium niobate crystal is used for the piezoelectric element, the cut angle α is -15 ° ≦ α ≦ + 25
カ ッ ト, and the cut angle β is −10 ゜ ≦ β ≦
Since the wafer 1 is cut so as to form + 10 °, a piezoelectric element having a high electromechanical coupling coefficient and extremely high temperature stability can be provided.

FIG. 2 is a diagram showing a configuration example of a piezoelectric element according to the present invention. Referring to FIG. 2, this piezoelectric element is made of a lanthanum gallium niobate crystal (La ₃ Ga _5.6 Nb _0.5
O ₁₄ crystal), that is, on the main surface of the piezoelectric plate 1 made of so-called langanite, at a predetermined interval Δx,
(2, 3) and an extraction electrode pair (4, 5) are arranged.

Further, the crystal axes of the lanthanum gallium niobate crystal are defined as X axis (electric axis), Y axis (mechanical axis), and Z axis, respectively.
Axis (optical axis), the rotation angle about the X axis (the cut angle of the crystal in the YZ plane (the counterclockwise angle from the Z axis in the YZ plane)) is α, and the rotation angle about the Y axis When (the cut angle of the crystal in the XZ plane (the counterclockwise angle from the X axis in the XZ plane)) is β, the piezoelectric plate 1 has Y
Xlb / α / β cut lanthanum gallium niobate crystal wafers have been used.

Here, a wafer having cut angles α and β of −15 ° ≦ α ≦ + 25 ° and −10 ° ≦ β ≦ + 10 ° is used for the piezoelectric plate 1. That is, the wafer 1 of FIG. 1 is used, and in FIG. 2, X ′ is the X ′ axis of FIG.
Z ′ corresponds to the Z ′ axis in FIG.

In the piezoelectric element having such a configuration, when a high-frequency voltage is applied as an input signal between the terminals 6, 6 'of one of the excitation electrode pairs (2, 3), the excitation electrode pair (2, 3)
The piezoelectric plate 1 of lanthanum gallium niobate crystal includes:
Distortion vibration corresponding to the high-frequency voltage, that is, shear elastic vibration is generated inside the piezoelectric plate 1 in the thickness direction of the piezoelectric plate 1.
That is, a high-frequency electric signal is converted into a mechanical vibration signal. When this vibration signal propagates through the piezoelectric plate 1 and reaches the extraction electrode pair (4, 5), a voltage is induced between the extraction electrode pair (4, 5). That is, a mechanical vibration signal is converted into an electric signal, and the induced voltage is used as an output signal as a signal at the terminal 7,
It can be taken out from between 7 '.

Here, the thickness H of the piezoelectric plate 1 is 0.1
is of the order of Mm～1.0Mm, the piezoelectric plate 1 X 'in the axial direction length W _x' is of the order of 5 mm to 20 mm, also, Z 'of the axial length of the piezoelectric plate 1 (Width) W _z 'is 5
is of the order of Mm～20mm, The area S of the piezoelectric plate 1 is of the order of 25mm ² ~400mm ^2. The length L _x ′ of each of the excitation electrodes 2, 3, and each of the extraction electrodes 4, 5 in the X′-axis direction is about 1 mm to 5 mm.
The length L _z ′ of each of the excitation electrodes 2, 3 and the extraction electrodes 4 and 5 in the Z′-axis direction is about 2 mm to 7 mm, and the distance between the excitation electrodes 2 and 3 and the extraction electrodes 4 and 5 is The gap Δx is 0.1
mm to about 0.4 mm. As for the shapes of the excitation electrodes 2 and 3 and the extraction electrodes 4 and 5, they may be semicircular as shown in FIG. 2, or may be rectangular. Alternatively, an arbitrary shape such as a semi-elliptical shape is also possible.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As one embodiment of the present invention, the inventor of the present application
Actually, a piezoelectric element (planar oscillator) using a wafer 1 of YX1b / α / β cut lanthanum gallium niobate crystal was prepared and its characteristics were examined. Here, wafer 1
Lanthanum gallium niobate crystals (La ₃ Ga
_5.6 Nb _0.5 O ₁₄ crystal), that is, so-called langanite, the cut angle α is set to −15 ° ≦ α ≦ + 25 °, and the cut angle β is set to −10 ° ≦ β ≦ + 10 °. The cutout was used to make it easier.

The size (size) of the wafer 1 is a small one having a length W _x ′ and a width W _z ′ of about 10 mm (area of about 100 mm ² ) and a thickness H of about 0.5 mm. And the respective excitation electrodes 2 and 3 and the respective extraction electrodes 4 and 5
The length L _x ′ is 2 mm and the width L _z ′ is 4 mm.
The distance Δx between the pair of excitation electrode pairs 2 and 3 and the pair of extraction electrode pairs 4 and 5 was set to about 0.2 mm. Then, a high-frequency voltage (for example, a high-frequency voltage having a voltage amplitude of about 1 V) is applied as an input signal between the pair of excitation electrodes 2 and 3 from the power supply 50, and the lanthanum-gallium-niobate is applied by the pair of excitation electrodes 2 and 3. Elastic waves were excited on the salt crystal wafer 1.

FIG. 3 shows the experimental results of the temperature characteristics (temperature dependence of the resonance frequency fluctuation Δf / f) of the piezoelectric element thus manufactured. In this experiment, four piezoelectric elements having a cut angle β of + 1.5 ° and a cut angle α of 6 °, 6.5 °, 7 °, and 7.5 °, respectively, of the langanite serving as the piezoelectric plate 1 were used. Using. From the experimental results of FIG. 3, the cut angle β
Is + 1.5 ° and the cut angles α are 6 ° and 6.5, respectively.
In each of the piezoelectric elements {, 7}, 7.5}, the temperature dependence of the resonance frequency fluctuation Δf / f of the excited elastic wave is small, and the oscillation frequency (resonance frequency) changes in the temperature range of −25 to + 75 ° C. Was 10 ^-4 or less. This characteristic is significantly better than similar characteristics of a conventional prototype piezoelectric element.

The following table shows the most commonly used crystal (AT
-Cut), lithium tetraborate, lithium tantalate X
- cut, langasite _{(La 3 Ga 5 SiO 14)} YX1 /
The characteristics of the resonance frequency fluctuation Δf / f and the electromechanical coupling coefficient K between each piezoelectric element of the 1.5 ° cut prototype and the piezoelectric element of the langanite (La ₃ Ga _5.6 Nb _0.5 O ₁₄ ) of the present invention were measured by experiments. It is a table | surface which shows the result. In addition, the cut angle of the langanite of the present invention used in Table 1 was YX1b / + 7.
{/+1.5}.

[0023]

[Table 1]

From Table 1, it can be seen that in the case of a quartz (AT-cut) piezoelectric element, the resonance frequency fluctuation Δf / f is very small at about 12 × 10 ^{−6 in} the temperature range of −25 ° C. to + 75 ° C., and the temperature stability is low. Although very high, the electromechanical coupling coefficient K is very low at 8%, which makes it difficult to manufacture a filter having a wide bandwidth and an oscillator having a large tuning range.

On the other hand, in a piezoelectric element of lithium tetraborate, lithium tantalate X-cut, and langasite YX1 / 1.5 °, the electromechanical coupling coefficient K is 14 to 20% in a temperature range of −25 ° C. to + 75 ° C. And is suitable for manufacturing a filter having a wide bandwidth and a resonator having a large tuning range, but the resonance frequency fluctuation Δf / f is 150 × 10 ^−6.
There is a drawback that the temperature stability is very large at about 350 × 10 ⁻⁶ and low.

On the other hand, the langanite piezoelectric element of the present invention has a temperature range of −25 ° C. to -25 ° C. compared to the lithium tetraborate, lithium tantalate X-cut, langasite YX1 / 1.5% piezoelectric element. The resonance frequency fluctuation Δf / f at + 75 ° C. is small (about 80 × 10 ⁻⁶ ,
The electromechanical coupling coefficient K is large (K = about 16%) as compared with a quartz (AT-cut) piezoelectric element, and therefore, the temperature stability is improved as compared with the conventional prototype piezoelectric element.
(Resonance frequency fluctuation is low), and it was confirmed that the electromechanical coupling coefficient K was increased. It should be noted that even in the case of a langanite piezoelectric element, the cut angles α and β are -15 ° ≦ α ≦ + 2
When it is not within the range of 5 °, −10 ° ≦ β ≦ + 10 °, the temperature stability sharply decreases.

From this, it can be seen that YX1b / α / β of the present invention
Has a cut angle α, β of −15.
When ゜ ≦ α ≦ + 25 ° and −10 ° ≦ β ≦ + 10 °, the temperature stability is greatly improved as compared with the prototype piezoelectric element, and the coupling coefficient is improved to some extent. It is the best element for many devices such as crystal filters, especially for mobile communication devices where the temperature change in frequency is <10 ^-4 and a frequency range of 0.2-1% is required.

[0028]

As described above, according to the first aspect of the present invention, there is provided a wafer obtained by cutting a lanthanum gallium niobate crystal by YX1b / α / β cutting,
When the crystal axes of the lanthanum gallium niobate crystal are X axis (electric axis), Y axis (mechanical axis), and Z axis (optical axis), the angle of the wafer from the Z axis in the YZ plane α
Forms counterclockwise −15 ° ≦ α ≦ + 25 °, and
The angle β from the X axis in the XZ plane is -1 in a counterclockwise direction.
It is cut out so as to form 0 ゜ ≦ β ≦ + 10 ゜,
When a piezoelectric element is manufactured using this wafer, for example, a piezoelectric element having high temperature stability and a high electromechanical coupling coefficient can be provided.

According to the second and third aspects of the present invention, the lanthanum gallium niobate crystal is made of YX1
A piezoelectric element using a wafer cut by b / α / β cut, wherein the crystal axes of a lanthanum gallium niobate crystal are X axis (electric axis), Y axis (mechanical axis), and Z axis (optical axis), respectively. ), The angle α from the Z axis in the YZ plane forms −15 ° ≦ α ≦ + 25 ° in the counterclockwise direction, and the angle β from the X axis in the XZ plane is counterclockwise. Since it is cut out so as to form −10 ° ≦ β ≦ + 10 °, it is possible to provide a piezoelectric element having high temperature stability and a high electromechanical coupling coefficient, signal selection and stabilization by frequency. It is particularly suitable for use in modulators, oscillators, narrow band and mid band bandpass filters.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration example of a wafer according to the present invention.

FIG. 2 is a diagram (perspective view) showing a configuration example of a piezoelectric element according to the present invention.

FIG. 3 is a diagram illustrating an example of a temperature characteristic of the piezoelectric element of FIG. 2;

[Description of Signs] 1 Piezoelectric plate 2, 3, 4, 5 Excitation electrode 6, 6 'Input terminal 7, 7' Output terminal

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Pisarevsky Yuriy Vladimirovich Russian Federation 117526 Moscow City Pull. Bernatkovo D. 105 Kei. 2 Kabe. 13 Tawalishi Chestvos Ogranichonnoy Ottovetsteven Naustino Komercheskaya Filma "Bunch" (72) Inventor Mill Boris Veniaminovich Russian Federation 117526 Moscow City Pull. Vernatskovo D. 105 Kei. 2 Kabe. 13 Tawalish Chestvos Ogranichonnoy Ottovetsteven Naustino Komercheskaya Filma “Bunch” (72) Inventor Sennecichenkov Pyotr Alex Sandrovich Russian Federation 117526 Moscow City Pull. Vernatskobo D. 105 Kei. 2 Kabe. 13 Tawalish Chestbos Ogranichonnoy Otobetstovenosutyu Nauchinokomercheskaya Filma “Bunch”

Claims (3)

[Claims] 1. A wafer obtained by cutting a lanthanum gallium niobate crystal by YX1b / α / β cut,
When the crystal axes of the lanthanum gallium niobate crystal are X axis (electric axis), Y axis (mechanical axis), and Z axis (optical axis), the angle of the wafer from the Z axis in the YZ plane α
Forms counterclockwise −15 ° ≦ α ≦ + 25 °, and
The angle β from the X axis in the XZ plane is -1 in a counterclockwise direction.
A wafer cut out so as to satisfy 0 ° ≦ β ≦ + 10 °. 2. A piezoelectric element using a wafer obtained by cutting a lanthanum gallium niobate crystal by YX1b / α / β cut, wherein a crystal axis of the lanthanum gallium niobate crystal is set to an X axis (electric axis). ), Y axis (machine axis), Z axis
(Optical axis), the angle of the wafer from the Z axis in the YZ plane is -15 ° ≦ α ≦ + 25 in a counterclockwise direction.
A piezoelectric element, which is cut out so that an angle β from the X axis in the XZ plane is -10 ° ≦ β ≦ + 10 ° in a counterclockwise direction. 3. The piezoelectric element according to claim 2, wherein the wafer has an excitation electrode pair for exciting an elastic wave and an extraction electrode pair for converting the elastic wave propagating through the wafer into an electric signal and extracting the electric signal. Are arranged side by side.